#include<stdio.h>

long staircase(long num)
{
    if(num == 1)
    {
        return 1;
    }
    if(num == 2)
    {
        return 2;
    }
    else
    {
        return staircase(num-1) + staircase(num-2);
    }
}

int main()
{
    int n;
    scanf("%d", &n);

    printf("%ld", staircase(n));

    return 0;
}
